OpenSSL is a framework which implements the secure socket layer. It ships with a program/library which gives you access to all those functions.

OpenSSL is a framework which implements the secure socket layer. It ships with a program/library which gives you access to all those functions.

LibreSSL is a version of the TLS/crypto stack forked from OpenSSL in 2014, with goals of modernizing the codebase, improving security, and applying best practice development processes.
Mbed TLS (formerly known as PolarSSL) makes it trivially easy for developers to include cryptographic and SSL/TLS capabilities in their (embedded) products, facilitating this functionality with a minimal coding footprint.
Ciphey aims to be a tool to automate a lot of decryptions & decoding's such as multiple base encodings, classical ciphers, hashes or more advanced cryptography. Automatically decrypt encryptions without knowing the key or cipher, decode encodings, and crack...

GnuTLS (the GNU Transport Layer Security Library) is a free software implementation of the SSL, TLS and DTLS protocols. It offers an application programming interface (API) for applications to enable secure communication over their network transport layer, as well as interfaces...
Network Security Services (NSS) comprises a set of libraries designed to support cross-platform development of security-enabled client and server applications with an option support for hardware SSL acceleration on the server side and hardware smart cards on the client side.
wolfSSL (formerly CyaSSL) is a small, fast, portable implementation of TLS/SSL for embedded devices to the cloud. http://www.wolfssl.com.